The primary physical hazards associated with hydrogen gas are its flammability and explosiveness. This is because hydrogen can form flammable mixtures in air over a wide range of concentrations (4% to 75%), and very low energy is needed to ignite hydrogen-air mixtures. Hence sensors are required to detect hydrogen leaks to warn of explosion hazards.
Existing sensors for detecting hydrogen use palladium metal (Zuttel, A.; Nutzenadel, Ch.; Schmid, G.; Chartouni, D.; Schlapbach, L. J. Alloys Compd. 1999, 472-475; Watari, N.; Ohnish, S.; Ishi, T. J. Phys. Condens. Matter, 2000, 12, 6799-6823) and palladium alloys (Hughes, R. C.; Schubert, W. K. J. Appl. Phys. 1992, 71, 542-544.) The disadvantage of using pure palladium based sensors is the irreversible phase change associated with exposure of palladium to hydrogen. This phase change causes thin films to delaminate from the sensor surface. The advantage of using palladium alloys, especially the Pd/Ni alloy, is the suppression of the phase transition. The response of the alloy materials is also very fast and reversible. The disadvantage of these films is that they require elevated temperatures to work well and are inhibited by oxygen.
Conducting polymers such as polyaniline (Huang, J.; Virji, S.; Weiller, B. H.; Kaner, R. B. Chem. Eur. J. 2004, 10, 1314-1319), polypyrrole (Ratcliffe, N. M. Anal. Chim. Acta 1990, 239, 257-262), and polythiophene (Ellis, D. L.; Zakin, M. R.; Bernstein, L. S.; Rubner, M. F. Anal. Chem. 1996, 68, 817-822) have been widely used to develop fast and efficient chemical sensors. Conducting polymers are highly desirable because they are inexpensive and easy to synthesize. Of the conducting polymer sensors, polyaniline appears to be the most widely studied due to its ease of synthesis and stability in air.
Janata, et al. (in Domansky, K.; Baldwin, D. L.; Grate, J. W.; Hall, T. B.; Josowicz, M.; Janata, J. Anal. Chem. 1998, 70, 473-481) have shown that a field effect transistor with 2 layers, palladium and polyaniline can be used as a good sensor for hydrogen. These sensors operate at 90° C. and display fast response times. Recently, it has been reported that conducting polymers may have some ability to store hydrogen. Cho, S. J.; Song, K. S.; Kim, J. W.; Kim, T. H.; Choo, K. Fuel Chem. Div. Prepr. 2002, 47, 790-791; Panella, B.; Kossykh, L.; Dettlaff-Weglikowska, U.; Hirscher, M.; Zerbi, G.; Roth, S. Synth. Met. 2005, 151, 208-210.
It would be useful to be able to provide a sensor that is not subject to the response limitations of conventional polyaniline. It would also be helpful to be able to provide a room temperature hydrogen sensor.